Difference Between Chemical Weathering and Mechanical Weathering

Chemical weathering and mechanical weathering form part of the natural processes that nature imposes on its subjects. Weathering happens when there is a breakdown, physical or chemical, to the surface mineral of rocks. This event is brought upon through natural elements such as water, gas, ice and plants.

Chemical Weathering

Rocks may decompose or dissolve and at the same time changes in composition through a certain chemical process to form residual materials. This is called chemical weathering. There are three very common chemical processes involved with chemical weathering. First is dissolution which occurs when water such as rain reacts with minerals and dissolving the rock changing its chemical composition. Oxidation is another process wherein oxygen reacts with the minerals in a rock, specifically iron, to form rust. This is why we sometimes see red-colored rocks. Hydrolysis takes effect when water reacts with Feldspar, the most common mineral in rocks, and forms another product, usually clay, that can be easily dissolved later on.

Mechanical weathering

Mechanical weathering happens when rocks disintegrate or breaks down into smaller pieces through physical forces which could be any of the following: exfoliation, abrasion and freeze and thaw weathering. Exfoliation happens when rock sheds off sheets of it along the sheet joints that form by applying pressure on the rock through natural causes such as tectonic activities. Abrasion occurs when rock surface weathers and removes layers of it through friction. The strong wind that constantly rubs on the rock’s surface eventually breaks it down causing it to reduce in size. In cold places where temperatures reach below zero degrees, water that accumulated and froze in between crevices of a rock expands. When time comes that water thaws, it gives more space for more water to sink inside the crevice, and will freeze again. Until such time that rock breaks along such crevice causing the rock to reduce into smaller fragments.

Difference between Chemical Weathering and Mechanical Weathering

Chemical and mechanical weathering are both natural processes that will break down rocks. Their purpose may be the same but their processes are different. Chemical weathering demands chemical reactions with minerals inside the rock and causes changes in rock composition. Sometimes this process will produce a different kind of product due to the reaction. Mechanical weathering only involves the physical breakage of rocks to smaller pieces of fragments. Without changing the physical composition of the rocks, mechanical weathering disintegrates rocks with nature’s own physical pressures.

Climate is very important in the weathering process. Cold temperatures favor mechanical weathering while warm temperatures support chemical weathering. And once weathering is complete, residual materials will be eroded and transported by either wind or water.

In brief:

• Chemical weathering happens when there is change in the composition of rocks through chemical processes and form residual materials. Processes include oxidation, dissolution, and hydrolysis.

• Mechanical weathering occurs when there is only physical change in rock structure such as size and shape through physical forces of nature. Processes include exfoliation, abrasion and freeze and thaw weathering.

• Climate is an important factor for weathering to take place. Cold temperatures favor mechanical weathering while warm temperatures support chemical weathering.